#pragma once

#include <boost/container/flat_set.hpp>
#include <cassert>
#include <utility>

// Using boost flat set was faster than std::set.

template <typename Field, typename Cluster>
auto make_empty(Field field, Cluster const & c){
	for(auto&& p : c){
		field.get(p) = 0;
	}
	field.collapse();
	return field;
}

namespace detail {
	template <typename Field>
	auto same_group(Field const & field, typename Field::Position const & p, typename Field::Position const & q){
		return field.get(p) == field.get(q);
	}

	template <typename Field>
	void cluster_expand(Field const & field, typename Field::Position const & p, boost::container::flat_set<typename Field::Position>& ret){
		for(auto&& q : field.neighbors(p)){
			if(!same_group(field, p, q)) continue;

			if(ret.insert(q).second){
				cluster_expand(field, q, ret);
			}
		}
	}
}

template <typename Field>
auto cluster_at(Field const & field, typename Field::Position const & p){
	boost::container::flat_set<typename Field::Position> ret;
	ret.reserve(10); // speed improvement of 20%
	ret.insert(p);
	detail::cluster_expand(field, p, ret);
	return ret;
}

template <typename Grid, typename Rules>
auto all_clusters(Grid const & grid, Rules const & rules){
	std::vector<decltype(cluster_at(grid, std::declval<typename Grid::Position>()))> ret;
	ret.reserve(10);
	auto partition = make_empty(grid, grid.all_positions());
	auto current_p = 1;
	for(auto&& p : partition.all_positions()){
		if(!partition.empty(p) || grid.empty(p)) continue;

		auto cluster = cluster_at(grid, p);
		for(auto&& q : cluster){
			partition.get(q) = current_p;
		}

		current_p++;
		if(cluster.size() >= rules.min_cluster_size()) ret.push_back(std::move(cluster));
	}

	return ret;
}